1. Technical Field
The present invention relates to a mandrel for bending a rectangular duct body and, more particularly, to a mandrel for bending a rectangular duct body, wherein when a rectangular duct body used for various purposes, such as a hanger arm connected to the trunk lead of a vehicle is bent in a specific shape, the rectangular duct body is partially depressed so that a bent part is prevented from being cracked and rollers that form the mandrel are smoothly rotated.
2. Description of the Related Art
As noted, in a hanger arm connected to the trunk lead of a vehicle or parts that form various types of mechanical tools, a rectangular duct body is bent in a specific shape using a bending machine. When bending the rectangular duct body, the bending work is performed by inserting a mandrel into the rectangular duct body in order to prevent the bent part of the rectangular duct body from being depressed.
From among mandrels used to prevent a phenomenon in which a rectangular duct body is depressed when bending the rectangular duct body using a bending machine as described above, there is a mandrel having a main body formed of a rectangular pole and having a front end rounded. When performing a bending work on the rectangular duct body using such a mandrel, the round part of the mandrel needs to be precisely matched with the bent part of the rectangular duct body. However, an accurate position of the mandrel cannot be seen outside because the mandrel is inserted into the rectangular duct body.
Accordingly, there is a disadvantage in that the rectangular duct body is depressed in the direction in which the bent part of the rectangular duct body is bent because the bent part of the rectangular duct body cannot be precisely matched with the round part of the mandrel. Furthermore, there are many disadvantages in the structure of the mandrel, such as that a range in which the rectangular duct body is applied to the parts of various types of mechanical tools is narrowed, because the rectangular duct body cannot be bent at various angles.
In order to solve the disadvantages, a mandrel including one roller or two rollers and a mandrel having a metal plate stacked thereon have been disclosed, thereby solving some of the disadvantages of the mandrel. In such mandrels, however, a crack is generated in a bent part because the entire bent part is not depressed.
Furthermore, there are many problems in the structures of conventional mandrels, such as that the lifespan of the mandrel is short and a bending work is not smoothly performed, because a lubrication action is not smoothly performed between rollers that form the mandrel and between the roller and the rectangular duct body.